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1920] 



LANGDON—DIOON SPIXULOSUM 



in 



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of the stem, and further, that these girdling strands are horizontal 



from the beginning and continue so throughout their whole extent. 



The investigation here described was undertaken with a view 



to supplementing Chamberlain's general account of the histological 



structure of the adult stem of D. spinulosum, especially by a careful 



study of the broad foliar rays or leaf gaps with their included 



traces, a phase of cycadean anatomy only slightly touched upon by 



earlier investigators. As the work has progressed, its scope has 



been extended to include the general course and organization of 



the foliar strands in the cortical part of both adult and seedling 



stems. 



Material and methods 



The adult wood and abundant material of two- and three-year- 

 old seedlings, which furnish the basis for this study, were secured by 

 Chamberlain from the Hacienda de Joliet near Tierra Blanca, 

 Mexico. The ten-year-old seedlings were from seeds procured in 



grown in the botanical 



the 



same 



locality but germinated and 



greenhouse of the University of Chicago. 



Preparation of all material of the adult stem for sectioning 

 was in the main as follows. Narrow, wedge-shaped sections 

 extending radially from pith to cortex were cut from both the 

 upper and lower portions of a trunk 18 ft. in height, care being 

 taken that each included two or more of the large medullary rays. 

 These sections were then cut into blocks about 1 cm. square, 

 some slightly larger, and kept in series. 



The various stages involved in the preparation of these blocks 

 for sectioning, namely, demineralization of the woody tissues 

 through the use of hydrofluoric acid, followed by a thorough 

 washing of the material in running water to free it from all traces 

 of the reagent, transference to various grades of alcohol and xylol, 

 and finally imbedding in paraffin, have been discussed in a previous 

 paper (8). Special care had to be taken in imbedding, the best 

 results being obtained when the blocks were carried through the 



process of infiltration with paraffin from 48 hours to 3 days. After 

 this they could easily be cut with a sliding microtome, and a com- 

 plete series obtained by removing each section, as cut, from the 

 knife and placing it directly upon the slide. Staining was with 



